If you’re reading this, you’ve likely discovered that mid-drive e-bike crank bolts can fail. Sometimes they fail because they were installed incorrectly: too much torque was applied, or the adhesive smeared on the bolt threads during initial installation was too strong, causing the bolt to break upon removal. Or sometimes they fail because the bolt threads may be damaged or just simply wear out. Whatever the circumstances are, you suddenly need to replace your crank bolts but then you have to ask yourself, “How do I choose the right crank bolts for my e-bike cranks?”
The first practical reaction would be to consult the motor manufacturer. This seems reasonable but most motor manufacturers partner with crank manufacturers (like Miranda) to produce cranks specifically designed to be compatible with their respective motors. These custom cranks are built to maintain the bike’s chainline with precision; the cranks are most often attached to the motor via one of the standard crank interfaces: ISIS, JIS, BNI, or Shimano’s interface. This essentially means that cranks spec’d for e-bike models will have bolts determined by the crank interface.
Miranda M15 self-extracting crank bolts
This brings you back to the original question of how to choose the right crank bolts for your e-bike cranks but now it gets easier. If your old crank bolt is still in one piece, go find yourself a ruler or a tape measure with millimeter measurements. You’ll want to measure the diameter of the bolt’s thread length, that’s to say measure the diameter of the threaded part of the bolt. If you have a caliper measuring tool, even better since that’ll eliminate any margin of error. The resulting number will yield the diameter you’ll need to look for in a replacement bolt.
Caliper Measurement Tool
If however, your crank bolts got lost or broken, you’ll need to do a little bit of sleeve-rolled sleuthing and find out what model cranks you have. To find out who manufactured the cranks, look on the interior side of the cranks where you may be able to find the manufacturer’s logo. From there it’s recommended to either consult the manufacturer’s website or to contact the manufacturer directly to find out what crank bolts you’ll need
For Miranda cranks, send us an email at email@example.com
One more bit of information you might need before you go searching for replacement crank bolts is the thread pitch. Nearly all e-bike crank bolts have metric threading (as opposed to Unified Thread Standard), which is indicated by the letter “M” preceding the bolt diameter. For example, Miranda’s e-bike crank bolts all feature metric threading.
We get that anything which keeps you off your bike should be easy and painless to resolve. Send us an email if this article sparks more questions because someone else might have the same question, which would help us improve our service to you.
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